Various control schemes are known to sense and diagnose a failure in a refrigeration unit. However, most such schemes can continue to operate the unit only if the failed component is not a critical input or output component of if there is an alternative component that can substitute for the failed one. Component redundancy increases the complexity as well as the cost of the control.
In U.S. Pat. No. 4,327,556, failure of the defrost heater in a refrigerator to cycle is detected by a microprocessor. In response to a failed heater, the microprocessor connects an override relay in circuit with the heater to cycle the heater on and off. This system, however, cannot continue to operate a refrigerator upon a failure of critical input components, such as a food compartment temperature sensor or temperature setting control, or upon a failure of any critical output component, such as a damper, that otherwise would result in spoilage of food.
In another type of refrigeration system, an internal diagnostics routine executed by a microprocessor tests the condition of a temperature sensor in the refrigerator. In response to a fault, i.e., an open circuited or short circuited sensor, the compressor is cycled on and off with a predetermined duty cycle to cool the fresh food and freezer compartments of the refrigerator. This system, although effective to prevent spoilage of food caused by a failed temperature sensor, is not capable of adequately preserving food in the event of other types of component failures, such as a failed baffle, or in the event of multiple component failures, such as a short-circuited temperature sensor and a stuck baffle occurring at the same time.
An object of this invention accordingly is to provide a method of and system for controlling a refrigerator to accommodate the failure of what is usually considered to be an essential input or output device in a manner that continues to preserve the food being stored.
Another more specific object of the invention is to provide a method of and system for detecting the failure of a baffle of a refrigerator and in response operating the refrigerator in a manner to continue to suitably preserve food.
A further object of the invention is to provide a method of and system for detecting multiple component failures in a refrigeration control, identifying the components failed and operating the refrigerator using non-failed components to continue to preserve food.
Another object is to provide an improved system for diagnosing failed critical components of a refrigerator, taking corrective action to continue to preserve food and generating an alarm to identify to service personnel the nature of the failure diagnosed.
An additional object is to provide a microprocessor implemented control for a refrigerator that diagnoses failed critical input and output components of the refrigerator and in response carries out control using non-failed components to continue to preserve food.
A still further object of the invention is to provide fault tolerant control of an appliance without requiring component redundancy.
There is a tendency for control components within a refrigerator to be exposed to sources of electrical noise and to develop internal noise as a result of thermal effects and deterioration over time. Failure diagnosis systems of the prior art have a tendency to misinterpret noise superimposed on a component as a valid signal having a particular instantaneous value and in response take inappropriate action.
A further object of the invention, therefore, is to provide in a refrigerator control system a method of and system for detecting a "noisy" control component.
A still further object is to provide a method of and system for controlling a refrigerator in a manner to continue to preserve food stored therein upon diagnosis of a "noisy" critical control component.